The invention relates generally to techniques for detecting contraband and, more particularly, to techniques for remotely detecting contraband using electromagnetic radiation in the terahertz range.
A wide variety of inspection systems are employed at various public or private installations, such as airports, for screenings persons, luggage, packages and cargo, to detect the presence of contraband (e.g., weapons, explosives and drugs). Such systems include metal detectors, X-ray based inspection systems, nuclear magnetic resonance based inspection systems, nuclear quadruple resonance based inspection systems, and so forth. These inspection systems have one or more of various limitations such as low reliability in detecting explosives and drugs (leading to high rates of false alarms), health risk to screeners and those being screened due to exposure to harmful radiation, long screening time (leading to decreased throughput at checkpoints), and so forth.
Electromagnetic radiation in the terahertz range (about 0.1 terahertz to 10 terahertz), or terahertz radiation, is now being used in the field of contraband detection. Terahertz radiation easily penetrates clothes, cardboard, leather and other non-conductive (non-metallic) materials and poses minimal health risk to subjects being scanned. Moreover, a wide variety of contraband, such as explosives, drugs, chemical and biological agents, and so forth, show strong spectroscopic signatures in the terahertz range. These unique properties offer significant advantages in the field of contraband detection. However, known terahertz inspection systems are of limited practical utility because of their high cost and limited range of scanning. Additionally, known terahertz inspection systems require lengthy scan times per person or per piece of baggage, thereby reducing the throughput and causing inconvenience to those being screened. The complicated detection schemes (such as homodyne or heterodyne detection schemes, or time domain spectroscopic detection techniques that need advanced data analysis to alert) or sophisticated image generation procedures further increase the time required for detecting contraband or otherwise clearing a person or parcel.
It is therefore desirable to provide an efficient, reliable, and cost-effective inspection system for remote detection of contraband. It is also desirable to provide inspection systems that enable rapid scanning of the subject.